Since the clinical use of nitrogen mustard as an anticancer agent in the 1940s for the first time in the world, numerous anticancer drugs have ever been developed. Actually, for example, antimetabolites such as 5-fluorouracil, antitumor antibiotics such as adriamycin, platinum complex such as cisplatin, and plant-derived carcinostatics such as vindesine have been subjected to clinical use.
However, most of these carcinostatics have significant side effects such as digestive disorders, myelosuppression and alopecia since they are cytotoxic also to normal cells. Due to the side effects, their range of application is limited. In addition, the therapeutic effects themselves are partial and short, in most cases.
Developments of new carcinostatics in place of these has been made; however, satisfactory results have not yet been obtained. Patent Documents 1, 2, 3 and 4 disclose that certain kinds of compounds have fibrosing inhibitory actions, antitumor actions and STAT3/5 activation inhibitory actions, respectively. However, it is not known whether the specific compounds of the present invention have an antitumor effect.